Process for producing a composite metallic article

ABSTRACT

A process is disclosed for producing a composite strip consisting essentially of a stainless steel layer and a brazing alloy layer metallurgically bonded together along a common interface. The process comprises heating under pressure a package consisting of a plate of stainless steel and a plate of the primary brazing alloy containing a thin foil of a second brazing alloy at the mutual interface of the stainless steel and primary brazing alloy to a temperature above the melting point of the second brazing alloy but below the melting point of the primary brazing alloy and below the recommended hot working temperature of the stainless steel, lowering the temperature of the package while still under pressure below the melting point of the second brazing alloy, removing the pressure and further lowering the temperature of the now bonded package below 900*F and above the martensitic transformation temperature, reducing the thickness of the package to a strip at temperatures above the martensitic transformation, and cooling the strip to ambient temperature. Alternatively, the process can comprise heating the steel alone to a temperature above its recommended solution heat treatment temperature, lowering the temperature to slightly above the melting point of the primary brazing alloy, applying under pressure a plate of the primary brazing alloy without the second lower melting brazing alloy lowering the temperature of the package under pressure after partial melting of the brazing alloy at the interface below the melting point of the brazing alloy, removing the pressure and further lowering the temperature of the new bonded package below 900*F and above the martensitic transformation temperature, reducing the thickness of the package to a strip at temperatures above the martensitic transformation, and cooling the strip to ambient temperature.

United States Patent 1191 Steigelrnan 14 1 Mar. 18, 1975 1 1 PROCESS FORPRODUCING A COMPOSITE [73] Assignee: W. M. Chace Company, Detroit,

Mich.

[22] Filed: Feb. 4, 1974 [21] Appl. No.: 439,221

Related US. Application Data [60] Continuation of Ser. No. 303,195, Nov.2, 1972, abandoned, which is a division of Ser. No. 138,779, April 29,1971, abandoned.

[52] U.S. C1. 148/12 E, 29/5272, 148/127 [51] Int. Cl 1323p 3/10 Fieldof Search 148/12 E, 127; 29/5272, 29/5274 [56] References Cited UNITEDSTATES PATENTS 2,267,34 12/1941 Schwartz 29/5274 2.718.690 9/1955 Ulam29/471.5

2,845,365 7/1958 Harris 29/527.7 X 1,173,811 3/1965 Dewey et 11....148/127 3.224.088 12/1965 McNelly 29/5274 X 3,615,290 10/1971 Talento143/127 3,652,344 3 1972 Kingsbury 148/127 Primary Examiner-W. StallardAttorney, Agent, or Firm-Norman J. OMalley; Donald R. Castle; John C.Fox

1571 ABSTRACT A process is disclosed for producing a composite stripconsisting essentially of a stainless steel layer and a brazing alloylayer metallurgically bonded together along a common interface. Theprocess comprises heating under pressure a package consisting of a plateof stainless steel and a plate 'of the primary brazing alloy containinga thin foil of a second brazing alloy at the mutual interface of thestainless steel and primary brazing alloy to a temperature above themelting point of the second brazing alloy but below the melting point ofthe primary brazing alloy and below the recommended hot workingtemperature of the stainless steel, lowering the temperature of thepackage while still under pressure below the melting point of the secondbrazing alloy, removing the pressure and further lowering thetemperature of the now bonded package below 900F and above themartensitic transformation temperature, reducing the thickness of thepackage to a strip at temperatures above the martensitic transformation, and cooling the strip to ambient temperature.

Alternatively, the process can comprise heating the steel alone to atemperature above its recommended solution heat treatment temperature,lowering the temperature to slightly above the melting point of theprimary brazing alloy, applying under pressure a plate of the primarybrazing alloy without the second lower melting brazing alloy loweringthe temperature of the package under pressure after partial melting ofthe brazing alloy at the interface below the melting point of thebrazing alloy, removing the pressure and further lowering thetemperature of the new bonded package below 900F and above themartensitic transformation temperature, reducing the thickness of thepackage to a strip at temperatures above the martensitic transformation,and cooling the strip to ambient temperature.

8 Claims, No Drawings PROCESS FOR PRODUCING A COMPOSITE METALLIC ARTICLECROSS REFERENCE TO RELATED APPLICATIONS This application is acontinuation of Ser. No. 303,195, filed Nov. 2, 1972, and'now abandonedwhich was a division of Ser. No. 138,779, filed Apr. 29, 1971, and nowabandoned. The Assignment was recorded on Apr. 29, 1971 on Reel 2733 andFrame O65.

BACKGROUND OF THE INVENTION Field of the Invention This inventionrelates to stainless steel alloys clad with brazing alloys. Moreparticularly, it relates to articles and processes for producingspecific composites of stainless steel and brazing alloys in 'stripform.

Stainless steel alloys that are martensitic at room temperature havecertain advantageous properties. The precipitation hardened martensiticstainless steels have properties which make them very advantageous forcertain applications such as jet engine parts, heat exchangers andcertain honeycomb structures. One of the significant problems offabrication of shaped articles from such alloys is that brazing alloysin the form of foil or wire have to be inserted between the stainlesssteel alloy and the metal to which the stainless steel alloy is to bebonded. The three components of stainless steel alloys, the brazingalloy and the metal are aligned and heated to at or near the meltingpoint of the brazing alloy resulting in relatively high assembly costs.

Although it is known to clad steels with brazing alloys, cladding tomartensitic stainless steels with certain brazing alloys is not believedto be known. Martensitic stainless steels are difficult to form intoshapes, thus if cladding is done by conventional means the clad materialcannot be readily shaped by cold metal working techniques. Recommendedhot rolling temperatures for certain stainless steels are above themelting point of most brazing alloys. Hot working at temperatures belowthis temperature often results in cracking.

It is believed, therefore, a shaped article of a martensitic stainlesssteel clad with a brazing alloy having a melting point below thetemperature recommended for hot rolling would be an advancement in theart. It is also believed a process for producing a relatively thinstainless steel strip clad with a brazing alloy from relatively thickstock of stainless steel would be an advancement in the art.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of this inventionto provide a laminate of a martensitic stainless steel and a brazingalloy having a melting point below recommended hot working temperatureof the stainless steel.

It is a further object of this invention to provide a process forproducing relatively thin stainless steel strip clad with certainbrazing alloys from a relatively thick stainless steel stock.

It is an additional object of this invention to provide a process forproducing relatively thin laminate of a precipitation hardenedmartensitic stainless steel and certain brazing alloys having meltingpoints below the recommended hot working temperature.

In accordance with one aspect of the invention, there is provided aprocess which comprises forming a laminated package by inserting a thinfoil of a secondary brazing alloy between the interfaces of a stainlesssteel alloy plate and a plate of a primary brazing alloy, heating thelaminated package to a predetermined temperature while under pressure.The primary brazing alloy has a higher melting point than the secondarybrazing alloy, thus, the predetermined temperature is above the meltingpoint of the secondary brazing alloy and below the melting point of theprimary brazing alloy and below the recommended hot working temperatureof the stainless steel alloy. Thereafter, the temperature is lowered tobelow the melting point of the second brazing alloy while the package isstill under pressure. The pressure is removed and the temperature of thenow bonded package is loweredbelow 900F, but above the martensitictransformation temperature. Thereafter, the package is reduced inthickness to a strip at temperatures above martensitic transformationtemperature and finally the strip is cooled to ambient temperatures.

In accordance with another aspect of this invention there is provided aprocess comprising heating a relatively thick layer of stainless steelalloy to a first temperature sufficient to cause solution treatment,cooling the alloy to a second temperature that is from about 50F toabout 200F below the first temperature, applying a layer of a brazingalloy to at least one major surface of the stainless steel while at thesecond temperature to achieve a bond along a common interface, coolingthe resulting laminate to a third temperature below 900F and above themartensitic conversion temperature, reducing the thickness of thelaminate while at the third temperature to produce a strip and coolingthe strip to ambient temperature phase.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For a betterunderstanding of the present invention, together with other and furtherobjects, advantages and capabilities thereof, reference is made to thefollowing disclosure and appended claims in connection with the abovedescription of some of the aspects of the invention.

Laminates of stainless steels and other alloys are generally prepared byhot rolling to form a laminate of the two materials. Propermetallurgical bonding of the alloy with the stainless steel occurs. Withmartensitic stainlesssteels the foregoing method is not practical sincetelnperatures required to achieve bonding without melting of many alloyswith the stainless steel is not high enough to allow hot working withinthe recommended range of temperatures. Such steels remain extremelydifficult to roll without severe cracking. The brazing alloys havemelting points below the recommended hot rolling temperatures. Bypracticing certain concepts within this invention a laminate consistingof a martensitic stainless steel and certain brazing alloys is provided.Additional process concepts can be used to provide a laminate strip ofessentially any stainless steel and a brazing alloy from largerthickness material. The advantages of the process of this invention aremore fully realized when laminates consisting of martensitic stainlesssteels and brazing alloys are provided. Major advantages are realizedwhen laminates consisting essentially of a precipitation hardenedmartensitic stainless steel and a brazing alloy having a melting pointbelow about 1800F is provided.

Martensitic stainless steels are the steel alloys containing chromium asthe major alloying element and are generally classified as the 400series. Precipitation hardened stainless steels such as 17-4 PH, areaged by heating at temperatures of from about'900 to about 1 l50F toachieve precipitation of certain metals at the grain boundaries toachieve certain desired structural properties.

The martensitic phase of stainless steels is formed upon cooling tobelow about 300F. It is necessary to heat the steel above about l900F toachieve any metal working, such as rolling, without metal damage. Uponcooling, the steel remains in the austenitic phase until it reaches atemperature below about 300F. As can be appreciated, conventionalapplication of a brazing alloy to form a laminate is virtuallyimpossible since most of the brazing alloys melt at temperatures belowabout 1900F. lf alloys were applied to a martensitic steel and thetemperature was raised above 1900F for hot rolling, the alloy wouldmelt.

The process of this invention provides for the manufacture of acomposite strip as generally defined in Metals Handbooks as beingproducts less than 0.185 inches thick and less than 24 inches wide.These strips are produced from thicknesses above 0.1875 inches andgenerally above about 0.5 inches. The brazing alloy has a melting pointbelow about 1800F or at least 50F below the temperature at which themartensitic steel is recommended for hot rolling. A typical brazingalloy is about 67% by weight copper, 24% by weight manganese and 9% byweight nickel. Other brazing alloys for heat-resistant stainless steelalloys having the desired melting points are known in the art. All thatis necessary is that the alloy has a melting point below about 1850F andwill metal lurgically bond with a martensitic stainless steel.

The thick stock such as a 1 inch thick plate of martensitic stainlesssteel is heated to about 100F below the melting point of the desiredbrazing alloy. A thin strip generally less than 10 mils thickness ofanother brazing alloy having a lower melting point than the desiredalloy is placed between the thick stainless steel and the desiredbrazing alloy. The material is held at the temperature for about 2 to 4hours and then raised to about 30 to 60F below the melting point of thedesired brazing alloy to achieve a laminate of the brazing alloy to thestainless steel. The bond will subsequently be improved upon rolling atlower temperatures.

The laminate is cooled to between 300F and 900F because at temperaturesabove 900F the precipitation of chromium carbides can occur and causesubsequent intergranular corrosion in the stainless steel. A temperaturerange of from about 650F to 900F is preferred. Temperatures below about300F are to be avoided since martensite transformation occurs. Thelaminate is reduced to the desired thickness of strip without crackingwhich would occur at intermediate temperatures by conventional meanssuch as rolling. Preferred thicknesses are generally from about 0.02inches to about 0.15 inches with thickness of from about 0.08 to about0.10 inches being especially preferred.

Alternatively, the process can comprise heating the steel alone to atemperature above its recommended solution heat treatment temperature,lowering the temperature to slightly above the melting point of theprimary brazing alloy, applying under pressure a plate of the primarybrazing alloy without the second lower melting brazing alloy, loweringthe temperature of the package under pressure after partial melting ofthe brazing alloy, removing the pressure and further lowering thetemperature of the now bonded package below 900F and above themartensitic transformation temperature, reducing the thickness of thepackage to a strip at temperature above the martensitic transformation,and cooling the strip to ambient temperature.

While the foregoing process has been described in relation to the use ofmartensitic stainless steel, the process is not so limited. The processcan be applied to any stainless steel thus offering an alternativemethod from those known in the prior art. Thus, if desired the stainlesssteel can be austenitic, ferritic or martensitic as well as the variousprecipitation hardened stainless steels.

While there have been described what are at present considered thepreferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed is:

1. A process for producing a strip of laminated material comprising:

a. heating a relatively thick layer of a stainless steel alloy to afirst temperature sufficient to solution treat the stainless steelalloy,

b. cooling said alloy to a second temperature from about 50F to about200F below said first temperature,

c. applying a layer of a brazing alloy to one surface of said stainlesssteel to achieve a bond along a common interface,

d. cooling the resulting laminate to a third temperature below about900Fand above the martensitic transformation temperature,

e. reducing the thickness of the laminate while at said thirdtemperature to produce a strip and f. cooling said strip to ambienttemperature.

2. A process according to claim 1 wherein the original thickness of saidstainless steel is greater than about 0.5 inches.

3. A process according to claim 2 wherein said first temperature isabove about 1900F, said second temperature is from about 1700F to about1850F and said third temperature is from about 300F to about 900F.

4. A process according to claim 3 wherein said stainless steel is amartensitic stainless steel.

5. A process according to claim 4 wherein said stainless steel is aprecipitation hardened stainless steel.

6. A process for producing a strip of laminated materials comprising:

forming a laminated package consisting essentially of a plate of astainless steel alloy, a primary brazing alloy and a thin foil ofasecondary brazing alloy between the interfaces of said stainless steelalloy plate and said primary brazing alloy plate by inserting said foilbetween said interfaces,

heating said package to a predetermined temperature above the meltingpoint of the secondary brazing alloy and below the melting point of theprimary brazing alloy and below the recommended hot working temperatureof the stainless steel alloy while said package is under pressure,

tion, and cooling the strip to ambient temperature.

7. A process according to claim 6 wherein said secondary brazing alloyhas a melting point below about 1800F and said primary brazing alloy hasa melting point below about l900F.

8. A process according to claim 7 wherein said stairr less steel is amartensitic stainless steel.

l l =l =l

1. A PROCESS FOR PRODUCING A STRIP OF LAMINATED MATERIAL COMPRISING: A.HEATING A RELATIVELY THICK LAYER OF A STAINLESS STEEL ALLOY T A FIRSTTEMPERATURE SUFFICIENT TO SOLUTION TREAT THE STAINLESS STEEL ALLOY, B.COOLING SAID ALLOY TO A SECOND TEMPERATURE FROM ABOUT 50*F TO ABOUT200*F BELOW SAID FIRST TEMPERATURE, C. APPLYING A LAYER OF A BRAZINGALLOY TO ONE SURFACE OF SAID STAINLESS STEEL TO ACHIEVE A BOND ALONG ACOMMON INTERFACE, D.COOLING THE RESULTINGLAMINATE TO A THIRD TEMPERATUREBELOW ABOUT 900*F AND ABOVE THE MARTENSITIC TRANSFORMATION TEMPERATURE,E. REDUCING THE THICKNESS OF THE LAMINATE WHILE AT SAID THIRDTEMPERATURE TO PRODUCE A STRIP AND F. COOLING SAID STRIP TO AMBIENTTEMPERATURE.
 2. A process according to claim 1 wherein the originalthickness of said stainless steel is greater than about 0.5 inches.
 3. Aprocess according to claim 2 wherein said first temperature is aboveabout 1900*F, said second temperature is from about 1700*F to about1850*F and said third temperature is from about 300*F to about 900*F. 4.A process according to claim 3 wherein said stainless steel is amartensitic stainless steel.
 5. A process according to claim 4 whereinsaid stainless steel is a precipitation hardened stainless steel.
 6. Aprocess for producing a strip of laminated materials comprising: forminga laminated package consisting essentially of a plate of a stainlesssteel alloy, a primary brazing alloy and a thin foil of a secondarybrazing alloy between the interfaces of said stainless steel alloy plateand said primary brazing alloy plate by inserting said foil between saidinterfaces, heating said package to a predetermined temperaturE abovethe melting point of the secondary brazing alloy and below the meltingpoint of the primary brazing alloy and below the recommended hot workingtemperature of the stainless steel alloy while said package is underpressure, lowering the temperature of the package, while still underpressure to below the melting point of the secondary alloy, removing thepressure and further lowering the temperature of the now bonded packagebelow about 900*F and above the martensitic transformation temperature,reducing the thickness of the package to a strip at temperatures abovethe martensitic transformation, and cooling the strip to ambienttemperature.
 7. A process according to claim 6 wherein said secondarybrazing alloy has a melting point below about 1800*F and said primarybrazing alloy has a melting point below about 1900*F.
 8. A processaccording to claim 7 wherein said stainless steel is a martensiticstainless steel.